| Results and Discussion The literature is well documented with the reports which indicate that GA3 induces Alpha-amylase activity in cereal endosperm (Paleg 1960, Varner 1964) but there are hardly any showing the differential behaviour of tall and dwarf forms of plants for such a system. (Gale & Marshall 1975). The results of present investigation clearly reveal that not only the initial amylase activity was high in dwarf but they also showed greater increase due to GA treatment (Fig. 1). This is well reflected on its products i.e. reducing and total sugars in the four wheat varieties (Table 1). Infact changes in the Alpha-amylase activity closely paralleled those in reducing sugars and total sugars (Fig. 2). Juliano & Varner (1969) also reported similar findings. It also lent credence to the contention that GA induced Alpha-amylase has considerable influence on the release of reducing sugar in invivo as well as in vitro. In the present investigation althought it was not attempted to but Paleg et al. (1962) and Filner & Varner (1967) confirmed that in wheat, GA induced amylase activity is due to de novo synthesis of the enzyme itself. It may be interesting to note that all the three dwarfs showed GA induced amylase activity but one of them, the triple dwarf. Moti failed to respond in protease activity (Kumar et al. 1982). On the otherhand, Fick & Qualset (1973) and Gale and Marshall (1975) reported certain dwarf wheats which were GA insensitive in releasing Alpha-amylase. The reducing sugars and the total sugars increased with the age of seedlings (Table- 2) for the obvious reason that sugars are indispensible for meeting energy requirement through respiration. Rizvi and Sirohi (1974) have also reported this phenomenon in wheat. In this study a significant positive correlation (r = .81) was found between reducing sugars and respiration. The varieties undertaken displayed different levels of amylase activity, reducing and total sugars as a response to GA. This may primarily be due to the internal levels of these substances and secondly due to responsiveness of verieties to applied GA. The responsiveness depends on starch content, pH, calcium levels, protolyte activity, besides, endogenous hormone levels (Briggs 1968). Incidently, GA like substances were higher in dwarf varieties than the tall variety in our study (Kumar 1977) and so were the level of amylase activity and reducing sugars. It may further be explicited (Fig. 3) that efficacy of different doses of GA3 (% over 00 GA3) at respective seedling age) was highest at 24 hours and lowest at 48 hours. Jones & Armstrong (1971) suggested that GA elicited Alpha-amylase resulting in high levels of reducing sugars provides a means of further regulation by end product inhibitions. Such and product in this metabolic system, gives an osmotic effect which may act to dampen Alpha-amylase activity. These sequences appear to have occurred during 24-48 hours in the present study. Thus, whereas the importance of Alpha-amylase in releasing sugars for meeting energy requirement for the manifestation of GA3 induced growth ean not be disputed, it is difficult to explain a system in which GA induced amylase activity is observed but growth is unexpressed. Exactly that has happened with the triple dwarf Moti (Kumar et al. 1982). Radley (1970) also reported certain such semi-dwarf wheat genotypes. Nevertheless, the response of GA to certain metabolic systems but not to other (Kumar & Baijal 1984,1985), clearly indicates that GA3 operates at different sites of action, simultaneously but selectively regulating the physiology of dwarfism. Acknowledgement The authors than Dr. Mike D. Gale of Plant Breeding Institute. Cambridge, U.K. for his valuable suggestions and Principal, Agra College, Agra for providing facilities. |
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